Heretofore, as a cutting tool used in perforation machining of workpieces, what is referred to as an indexable drill has been used, which removably attaches a cutting insert having cutting edges at its tip on the distal side of the drill body. With this indexable drill, it has only been possible to conduct repetitive machining by replacing the cutting inserts provided with cutting edges, which become worn by the cutting of workpieces.
With respect to this type of indexable drill, at the tip of an approximately cylindrical rod-like drill body which rotates around an axis is formed a recessed part (cutting insert mount) which is recessed toward the proximal side, a cutting insert is fitted into this recessed part, and the drill body and cutting insert are integrated (e.g., see Japanese Registered Utility Model No. 3054444). In this indexable drill, on the inner surface of the recessed part of the drill body are formed a bottom face which faces the distal side, and which is orthogonal to the axis of the drill body, a pair of clamp faces which arranged on mutually opposing sides sandwiching the axis so as to face the inner circumferential side of the drill body while crossing this bottom face, and which clamp and hold the cutting insert, and torque transmission faces which arranged on mutually opposing sides sandwiching the axis so as to face the forward side of the drill rotation direction and which transmit the rotary force of the drill body to the cutting insert. Moreover, the paired clamp faces are respectively crossed by and adjacent to the paired torque transmission faces facing the backward side of the drill rotation direction from the inner circumferential side of the drill body.
The cutting insert has cutting edges formed at the tip of its insert body which is formed from cemented carbide such as sintered hard alloy. Furthermore, it forms on its proximal side a pair of clamp receiving faces which fit into the recessed part of the drill body and which receive the clamping force from the pair of clamp faces, and torque receiving faces to which are transmitted the rotary force of the drill body from the pair of torque transmission faces. The paired clamp receiving faces are respectively crossed by and adjacent to the paired torque receiving faces.
In this indexable drill, the crosshatch angles of the clamp faces and torque transmission faces of the drill body and the crosshatch angles of the clamp receiving faces and torque receiving faces of the cutting insert are equal, and fit together to integrate.
At the same time, in the indexable drill, a slit is formed in the drill body which extends from the bottom face in the axial direction on the proximal side so as to include the axis and parallel the axis, and the distal side of the drill body is divided into two parts which are respectively provided with one each of the clamp faces and torque transmission faces (e.g., see Japanese Unexamined Patent Application, First Publication No. 2004-330391). In this type of indexable drill, an insertion hole is formed so as to extend across the slit, and spiral machining of a female screw is conducted on the inner face thereof. By screwing a male screw member (clamping screw) into this insertion hole, it is possible to vary the size of the interstice of the slit. In short, it is possible to elastically deform the bifurcated tip parts and vary the interstice between the opposing faces of each tip part according to the depth to which the male screw member is screwed into the insertion hole. By this means, it is possible to have the clamp faces firmly press the clamp receiving faces of the cutting insert that is inserted into the recessed part of the drill body, and to clamp and hold the cutting insert.
Moreover, in the insertion hole, a screw part is provided which is contacted by the head of the clamping screw when said screw is loosened. By having the head contact this screw part, it is possible to enlarge the interstice of the slit, and facilitate attachment and removal of the cutting insert in the recessed part of the drill body.
However, with the aforementioned indexable drill, as the crosshatch angles of the clamp receiving faces and torque receiving faces of the cutting insert are identical to the crosshatch angles of the clamp faces and torque transmission faces of the drill body, the problem arises that if these faces are not formed with a high degree of accuracy, it may happen that adherence between these faces is impaired, that the transmitted clamping force is reduced, and that attachment rigidity of the cutting inserts in the drill body cannot be fully maintained. Furthermore, in such cases, there is the problem that the mutual axes of the drill body and cutting insert may be deviated during attachment of the cutting insert. Accordingly, when such problems occur, they result in impairment of the accuracy of machined holes.
Moreover, in the aforementioned indexable drill, the clamping screw which changes the size of the interstice of the slit and the female screw of the insertion hole into which is screwed the screw part contacted by the head of the clamping screw are female screws which both have the same direction as, for example, a right-hand screw. Consequently, when the clamping screw is loosened whereby the head of the clamping screw is made to contact the screw part in order to enlarge the interstice of the slit, there is the problem that the screw part is driven by the rotation of the clamping screw. In such cases, there is the problem that it may happen that the screw part is removed from the insertion hole, that the interstice of the slit cannot be enlarged, and that the cutting insert cannot be suitably attached and removed.
Furthermore, as the slit is open in the state where the cutting insert is integrated with the drill body, there is the problem that a resonance phenomenon occurs inside the space formed by the slit during cutting, and that a very loud cutting noise occurs. It may also happen that chip is ingested by the slit, damaging the inner face of the machined hole.
In addition, with the aforementioned indexable drill, when, for example, stainless steel material or the like is subjected to cutting, it may happen that a strong tightening force is imposed on the drill from the machined hole, and that cutting resistance becomes large, impeding the conduct of stable cutting. Furthermore, even when the drill body is withdrawn after formation of the machined hole, there is the problem that interference with the machined hole may occur, rendering it impossible to suitably withdraw the drill.
In light of the foregoing circumstances, the primary object of the present invention is to offer an indexable drill which is capable of suitably integrating the drill body and cutting insert with a high degree of attachment rigidity and attachment accuracy.
Moreover, a second object of the present invention is to offer an indexable drill which enables suitable attachment and removal of the cutting insert relative to the drill body, without having the screw part driven by the rotation of the clamping screw.
Furthermore, a third object of the present invention is to offer an indexable drill which effects mitigation of cutting noise during cutting, and which prevents damage to the machined hole from the ingestion of chip into the slit.
In addition, a fourth object of the present invention is to offer an indexable drill which enables the conduct of stable cutting by mitigating cutting resistance during cutting and interference during withdrawal.